This application claims the priority of German Patent Application, Ser. No. 100 13 479.3, filed Mar. 18, 2000, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a valve timing control apparatus for an internal combustion engine, and more particularly to a valve timing control apparatus for application as a hydraulic camshaft adjustment device of rotary piston type configuration.
German Pat. No. 197 26 300 A1 describes a valve timing control apparatus as so-called rotation-type adjustment device which includes a drive shaft, configured as outer rotor in driving relationship with a crankshaft of the internal combustion engine, and an impeller, configured as inner rotor and mounted in fixed rotative engagement on the camshaft of the internal combustion engine. The drive wheel defines a hollow space, which is demarcated by a cylindrical peripheral wall and two sidewalls, for accommodating the impeller. The hollow space is divided in three hydraulic working chambers formed by three boundary walls extending inwardly from the peripheral wall in the direction of the center axis of the drive wheel. The impeller has thus three vanes radially extending from a hub into the working chambers of the drive wheel. As a consequence, each working chamber is subdivided into two hydraulic pressure compartments which are fluidly sealed from one another by seals, disposed between the hub of the impeller and the boundary wall of the drive wheel as well as between the free end face of each vane of the impeller and the inner wall surface of the peripheral wall of the drive wheel. When hydraulic fluid is admitted selectively or simultaneously into the pressure compartments, the impeller is rotated or fixed in place with respect to the drive wheel and thus the camshaft is rotated or fixed in place relative to the crankshaft. A torsional spring, disposed in a separate space, extends between the impeller and the drive wheel for applying auxiliary energy to match different adjustment speeds, resulting from the camshaft friction, in both rotation directions of the device, on the one hand, and to rotate the camshaft into a base or starting position that is preferred at the start of the internal combustion engine, after the internal combustion engine has been shut down or in the event the pressure of the hydraulic fluid in insufficient to adjust the apparatus. The camshaft is held in the starting position during start of the internal combustion engine in addition by a separate locking mechanism for mechanically coupling the impeller with the drive wheel. The locking mechanism is substantially configured as stopper, which is resiliently received in a vane of the impeller and axially shiftable in a pocket of a sidewall of the drive wheel, with the stopper hydraulically connected with the pressure compartments of the apparatus and releasable when the apparatus is acted upon by hydraulic fluid again.
This conventional valve timing control apparatus suffers shortcomings because matching of the adjustment speeds and the rotation of the camshaft into the starting position of the camshaft at start of the internal combustion engine is realized by an additional spring, resulting in a significant increase in size of the axial installation space. In order to apply the required torque, the spring must be sized accordingly, and thus needs sufficient space, which may lead up to a doubling of the necessary axial installation space. Moreover, the spring represents an additional component so that fabrication and assembly results in an increase of production costs of the valve timing control apparatus. Another drawback is the required separate locking mechanism for implementing a mechanical coupling between the impeller and the drive wheel to hold the starting position of the camshaft during start of the internal combustion engine, because the resiliently supported stopper is also composed of a plurality of additional components and thus complicates the fabrication and assembly and ultimately to higher production costs for the valve timing control apparatus.
It would therefore be desirable and advantageous to provide an improved valve timing control apparatus, which obviates prior art shortcomings and is simple in structure and yet reliable in operation.
According to one aspect of the present invention, an apparatus for adjusting a rotational relation between a camshaft and a crankshaft of an internal combustion engine, includes a drive wheel configured as outer rotor in driving relation with the crankshaft and including a cylindrical peripheral wall and two sidewalls for formation of a hollow space which defines at least one hydraulic working chamber demarcated by two boundary walls extending inwardly from an inner wall surface of the peripheral wall in the direction of the center axis of the drive wheel, a rotatable impeller mounted in fixed rotative engagement with the camshaft and configured as inner rotor fitted in the hollow space of the drive wheel and having a wheel hub and at least one vane extending radially out from the wheel hub into the working chamber of the drive wheel to thereby subdivide the working chamber in two hydraulic pressure compartments acting in opposition to one another through selective or simultaneous admission of hydraulic fluid to thereby effect a rotation or fixation of the impeller with respect to the drive wheel and thus of the camshaft relative to the crankshaft, and a seal, positioned between a free end face of the vane of the impeller and the inner wall surface of the peripheral wall of the drive wheel, for fluidly sealing the pressure compartments from one another, with the seal formed by a roller-type sealing member spring-mounted in radial direction in an axial groove, wherein the inner wall surface forms for the sealing member a slanted ramp surface which extends radially outwards in a rotation direction of the impeller, so that a torque is transmittable onto the impeller by a tangential force component resulting from a combination of the slanted ramp surface of the drive wheel and a radial spring force of the sealing member applied upon the impeller, thereby matching adjustment speeds of the apparatus in both rotation directions during operation of the internal combustion engine and automatically rotating the impeller into a desired starting position of the camshaft, when shutting down the internal combustion engine, thereby mechanically coupling the impeller and the drive wheel, when the camshaft is in the starting position.
According to another feature of the present invention, the coupling between the impeller and the drive wheel can be released through suitable admission of hydraulic fluid into the respective one of the pressure compartments.
According to another feature of the present invention, all seals arranged at the vanes of the impeller may be formed as spring-biased roller-type sealing members and accordingly all portions of the inner wall surface of the peripheral wall of the impeller in the working chambers may be configured as radially outwardly extending ramp surfaces. Such construction results in an increase of the effective mean torque acting on the impeller. Of course, depending on the number of vanes of the impeller, it may also be possible to configure only seals of some vanes as roller-type sealing members and to configure the pertaining portions of the inner wall surface of the peripheral wall of the impeller as outwardly extending ramp surfaces to implement an effective mean torque. Further measures, such as modification of the ramp angle of the ramp surfaces and/or modification of the radial spring force of the sealing members may also be used to suit the effective means torque to conditions of the internal combustion engine at hand.
According to another feature of the present invention, the roller-type sealing members may be supported upon the vanes of the impeller by slide shoes having a top side, formed as a half-round bearing shell, and a bottom side acted upon by a spring. Thus, despite the relatively high radial spring force applied by the springs for urging the sealing members against the inside wall surface of the peripheral wall of the impeller, the configuration of the top side of the slide shoes as bearing shells as well as the lubrication by means of the hydraulic fluid ensure that the sealing members properly roll along the ramp surfaces and are prevented from jamming.
Suitably, the springs are configured as helical compression springs which are fitted in radial boreholes in the vanes of the impeller, with the boreholes terminating at the axial groove of the sealing members, for accommodating the spring. Helical compression springs are suitable as relatively high forces can be realized when being accordingly sized so that the magnitude of the mean torque applied upon the impeller can be suited to the situation at hand. Of course other constructions of spring elements are possible as well, such as, for example, chimney springs or elastomeric spring-type cushions, received in respective receptacles in the vanes of the impeller.
According to another feature of the present invention, the axial groove may have a width, which substantially corresponds to a diameter of the sealing member and exceeds a diameter of the borehole. In this way, sealing gaps are formed between the sealing members and the groove walls of the axial grooves to allow the required turning of the sealing members during rotation of the impeller, on the one hand, and to prevent fluid leakages between the pressure compartments of the hydraulic working chambers via the axial grooves. The depth of the axial grooves is suitably so sized that the sealing member can be almost entirely received therein so as to avoid a contacting of the slide shoes upon the groove base, when the sealing members are positioned at the radially innermost area of the ramp surface. This position normally corresponds to one of the two end positions of the vanes of the impeller upon the boundary walls of the drive wheel, whereby in this end position the spring elements of the sealing members apply a greatest spring force and thus realize a maximum torque upon the impeller.
According to another feature of the present invention, the ramp surfaces are formed with a depression in a region of a rotation position of the impeller corresponding to the desired starting position of the camshaft, for reinforcing a holding moment of the sealing member, resulting from the coupling of the impeller with the drive wheel by force, by an additional positive engagement. The depression may be formed as a stepped recessed axial area having a slanted transition at a juncture to the ramp surface. Taking into account the width of the vanes of the impeller, the recessed area is so arranged that the impeller is blocked in one rotation direction through abutment of its vanes upon the boundary walls of the drive wheel, whereas the other rotation direction of the impeller is barred in positive manner through impact of the sealing members upon the slanted transitions as well as in non-positive manner through the spring force of the spring elements of the sealing members.
In accordance with a variation, the depression may also be configured as an axial trough having a hemispherical profile at a radius corresponding to a radius of the sealing member. The depression is incorporated in the ramp surface such that the impeller can be locked in place in both rotation directions, shortly before impact of the vanes upon the boundary walls, in positive manner through engagement of the sealing members in the troughs as well as in non-positive manner by the spring force applied by the spring elements upon the sealing members.
Regardless of the configuration of the local depressions in the ramp surfaces, the impeller is coupled with the drive wheel only when the hydraulic pressure fails to adjust the impeller, e.g. at shutdown of the engine, so that through admission of hydraulic fluid into the pressure compartment that is of minimum volume at coupling position of the impeller, the coupling of the impeller with the drive wheel is reversed again hydraulically.
A valve timing control apparatus in accordance with the present invention has many advantages compared to conventional apparatuses. The need for a separate spring element that significantly enlarges the axial installation space is eliminated to provide the required auxiliary energy between the impeller and the drive wheel for matching the adjustment speeds of the apparatus and for rotating the camshaft into the starting position desired at the start of the internal combustion engine. Rather, the transmission of a torque upon the impeller is implemented in accordance with the present invention by a tangential force component resulting from the slanted ramp surface of the drive wheel and the radial spring force of each roller-type sealing member. Thus, space demands for an additional spring element are reduced and fabrication of such a separate spring element is avoided so that fabrication and assembly costs can be significantly reduced. By integrating in the function of the sealing members and the ramp surfaces at the same time the function of a locking mechanism to mechanically couple the impeller with the drive wheel in the starting position of the camshaft, the need for a separate locking mechanism and the ensuing complexity in conjunction with fabrication and assembly can be saved and the production costs can be further reduced.